It is well known, that the amount of waste waters being produced has been increasing all over the world, as have the number of waste water varieties. Waste water runoffs running into soil and fresh waters cause serious environmental damages, and therefore their efficient purification is vitally important. However, in spite of all current efforts, only a relatively small part of the total amount of waste waters produced ever arrives at purification plants for treatment.
While water networks and consumption shown an upward trend in some areas, waste water purification capacities are usually either not available at all, or insufficient. Moreover, efforts aimed at intensifying existing waste water treatment capacity have not yielded any significant results, partly due to the high cost of investment required and partly due to the sluggishness of currently recommended methods.
Known processes used for purification of communal and other waste waters containing organic impurities are based on biological decomposition.
In the course of the treatment in various apparatuses in several steps and in several engineering structures (sandtrap, precipitator, aerator, after-precipitator, sludge treatment apparatus, etc.) the organic and inorganic impurities present in the waste water are transformed, utilized, and built-in by microorganisms propagated in the treatment system. A major part of the living organisms form a certain part of the waste water sludges, requiring further anaerobic or aerobic biological treatment. The need for this anaerobic treatment calls for additional engineering structures and involves considerable excess expendi-ture.
Because of the fairly long time required for the treatment of waste water with biological processes, a volume capacity well exceeding the volume corresponding to the daily amount of waste water arriving at the plants has to be available for optimal purification efficiency. But at the same time, waste water movement and aeration necessary to realize the conditions required for the bio-logical proceses can be solved with electric power-operated heavy-duty machinery. Even so, due to such factors, the specific cost of investment in biological waste water purification plants is very high. Moreover, the lower the purification capacity of the plant to be built, the higher the specific cost of investment required.
As complements to biological purification processes, secondary or tertiary chemical treatments are sometimes used, so that non-biologically or only partly decomposable com-ponents of the waste water are removed. In this regard, chemicals used for the purification of drinking water in-clude aluminum sulfate, lime milk, trivalent iron salts, polyelectrolytes, etc. Such chemicals are also used for the purification of the waste waters as well.
Industrial waste waters which do not, or mostly do not, contain organic impurities are commonly treated by mixing various chemicals with the waste water. The purpose of mixing in the chemicals is to neutralize and bind the chemicals passing from the industrial processes, before they enter into the waste water.